The present invention relates to optical media, and more particularly to recording data on optical media.
Optical drives capable of recording data on optical media are well known in the art. These drives include the Compact Disc-Read/Write (CD-R) drives, which can read CD-based formats and read and write to Write Once Media, and Compact Disc-Rewritable (CD-RW) drives, which can read CD-based formats and read and write to Write Once Media and Rewritable Media. The standard CD recordable and rewritable media and format is set forth in what is commonly referred to in the art as the xe2x80x9corange bookxe2x80x9d. Under the standard, the writing of data is described in terms of xe2x80x9cTxe2x80x9d, where T is a fundamental unit of time, and has a minimum mark of 3T and a maximum mark of 11T. The length of T is determined by the speed of the clock, where with a 1xc3x97 optical drive, T=231 ns. The writing of the 3T mark is the most critical due to its size, thus the standard sets forth when to heat and cool the recording material in writing the 3T mark. A Non-Return to Zero Inverted (NRZI) method of recording is used, where a zero is represented by a change in the write control signal and a one by no change. When the write control signal first changes, the heating of the media begins. When the write control signal changes again, the heating ends, and the media is cooled to end the mark. When the media is heated and cooled to form a 3T mark varies with the type of media, and is set by the standard. However, the precision of the standard may be inadequate for higher recording speeds, such as 5xc3x97 or up. At these higher recording speeds, T becomes smaller, thus the writing must be more accurate to avoid compromising the reliability of the data. As the recording speed increases, the heating up and cooling time shrinking of the recording media causes different effects as the data goes from one type of mark into another type of space and vice versa. This causes the unreliable formation of mark and space lengths, especially when the recording media varies from one manufacturer to another.
One conventional method of increasing the writing accuracy is to fine tune the write control by using a faster clock. By using a clock with a cycle less than T, adjustments may be made at increments equal to a cycle of the clock while maintaining T at the same length. The faster the clock, the finer the adjustments. However, at the faster recording speeds, the required clocks would need to be very fast. Such fast clocks are very expensive, and their use increases the cost of manufacturing the optical drive.
Accordingly, there exists a need for a method and system for providing timing adjustment to perform reliable optical recording at high speeds. The method and system should avoid the need to have an expensive fast clock, thus avoiding an increase in the cost of manufacturing the optical drive. The present invention addresses such a need.
The present invention provides a method and system for providing timing adjustments to perform reliable optical recording at high speeds. The present invention includes performing a timing adjustment in a coarse increment to a write control signal using a clock with a cycle less than T, where T is a fundamental unit of time for a data mark; and performing a timing adjustment in a fine increment to the write control signal using a time delay technique. The method and system in accordance with the present invention provides a write control logic which allows for multiple levels of time adjustment for each type of mark. In the preferred embodiment, a dual level timing adjustment technique is provided. The first level provides coarse timing adjustments using a clock with a cycle less than T and parameters to control the power level and time duration of each mark. The second level provides fine timing adjustments using time delay techniques. By using the first and second levels of adjustments together, fine adjustments are provided without the need for expensive fast clocks. The method and system in accordance with the present invention thus allows for the writing of data at high speeds without compromising data reliability and without increasing the cost of manufacturing the optical drive.